Liquid crystal display (LCD) devices control whether light is transmitted or blocked (whether the display is on or off) by controlling the alignment of birefringent liquid crystal molecules.
Various liquid crystal alignment modes are utilized in LCD devices. Examples include: the twisted nematic (TN) mode in which liquid crystal molecules that exhibit positive dielectric anisotropy are aligned such that they twist 90° when viewed from the normal direction with respect to the substrates; the vertical alignment (VA) mode in which liquid crystal molecules that exhibit negative dielectric anisotropy are aligned perpendicularly to the substrate surfaces; the in-plane switching (IPS) mode in which liquid crystal molecules that exhibit positive dielectric anisotropy are aligned horizontally with respect to the substrate surfaces and a horizontal electric field is applied to the liquid crystal layer; and the fringe field switching (FFS) mode.
Liquid crystal display devices typically include an array substrate, a color filter substrate, and a liquid crystal layer sandwiched between this pair of substrates (the array substrate and the color filter substrate), for example. An alignment film may be applied to the surfaces of both substrates that are in contact with the liquid crystal layer.
An example of a method for manufacturing a liquid crystal display device will be described below. First, a plurality of spacers made of an insulating material are formed on one of the abovementioned substrates, and the substrates are fixed to one another. When a dripping method is used, a liquid crystal material is dripped in between the substrates before they are fixed together. When a vacuum injection method is used, the liquid crystal material is vacuum-injected between the substrates after they are fixed together, and then the injection hole is sealed. Next, polarizing plates, phase difference films, or the like are applied to the surface of each substrate opposite to the surface that is in contact with the liquid crystal layer, thereby completing the liquid crystal display panel. Finally, components such as a gate driver, a source driver, and a display control circuit are connected to the liquid crystal display panel, and a backlight or the like is provided, thereby completing the liquid crystal display device.
In recent years, technologies in which polymer layers (PSA layers) that control the alignment of the liquid crystal molecules and are formed either on top of the alignment film or directly on the substrates (if the substrates do not have an alignment film) have attracted attention. The PSA layers are formed by inserting a liquid crystal composition containing a liquid crystal material and a polymerizable ingredient such as a monomer or oligomer in between the substrates and then applying heat or irradiating the assembly with light (such as UV light) to polymerize the polymerizable ingredient (the monomer, oligomer, or the like).
Patent Document 1 discloses sandwiching a liquid crystal material into which a photopolymerizable compound is mixed between substrates on which photoalignment films are formed, and then irradiating the assembly with light to polymerize the photopolymerizable compound, thereby forming polymer sustained alignment layers. In Patent Document 1, the photoalignment films are alignment films that contain a polymer having a main chain and a side chain that includes a photoreactive functional group. These alignment films can be formed in a plurality of regions such that when the films are irradiated with light from different directions, the resulting alignment-restraining forces applied to the alignment films occur in different directions as well. Irradiating the photoalignment films with light causes impurities to form. However, the polymer sustained alignment layers fix the impurities in place and prevent impurity ions from entering the liquid crystal layer, thereby maintaining the pretilt angle of the liquid crystal molecules, preventing a reduction in voltage holding ratio, and inhibiting occurrence of burn-in.
Patent Document 2 discloses injecting a liquid crystal composition containing a polymerizable monomer in between the substrates and then irradiating the assembly with UV light while applying a voltage to transparent and oppositely disposed electrodes provided on the substrates. This polymerizes the monomer, thereby reducing occurrence of burn-in in the liquid crystal display device as well as resulting in the monomer having one or more ring structures or fused ring structures and two functional groups that are directly bound to the ring structures or fused ring structures.